1. Technical Field
The present invention relates to an exhaust pipe for a vacuum exhaust system, which is used for creating a vacuum in a vacuum chamber of, for example, a semiconductor manufacturing apparatus. More specifically, the present invention relates to an exhaust pipe having a means for preventing deposition of a reaction by-product on an inner surface of the exhaust pipe. The present invention also relates to a method for preventing deposition of a reaction by-product on an inner surface of an exhaust pipe.
2. Description of the Related Art
In a reduced-pressure chemical vapor-phase growth (CVD) apparatus, a reaction furnace (a vacuum chamber) in the form of a pipe made of quartz is provided, and a vacuum pump is connected to the reaction furnace through a metallic exhaust pipe. In such a reduced-pressure chemical vapor-phase growth apparatus, especially when it is applied to a process for forming an oxide film or a nitride film on a semiconductor substrate, a reaction by-product is produced in a large amount. The vacuum pump is contaminated with such a reaction by-product, with the result that the vacuum pump is likely to become inoperative in a short period of time. In order to avoid such a problem, a cleaning operation must be periodically conducted. However, such a requirement gives rise to a problem that an operative state of a reduced-pressure chemical vapor-phase growth apparatus is limited to a low rate.
To prevent a vacuum pump from becoming inoperative due to contamination with a reaction by-product, various types of traps that are provided in an exhaust pipe between the reaction furnace and the vacuum pump have been developed. Such traps are, to some extent, effective. However, in an exhaust pipe situated between the reaction furnace and the trap, there remains a problem of deposition and accumulation of a reaction by-product on an inner surface of the exhaust pipe. As a countermeasure, there has been proposed a heater in a spiral form provided on an outer surface of the exhaust pipe, so as to heat the exhaust pipe and therefore prevent condensation and deposition of reaction by-products on the inner surface of the exhaust pipe.
However, this method remains unsatisfactory, since heat generated by the heater escapes into the atmosphere and therefore the temperature of the exhaust pipe cannot be increased in an efficient manner. Especially, in a process for forming an oxide film, a sublimation temperature of the reaction by-product is high, and an amount of a reaction by-product is large, with the result that deposition of a reaction by-product cannot be effectively prevented.